1. Field of the Invention
The present invention relates to a hard coating that is used for a glass molding die, and has excellent mold releasability with respect to glass after high-temperature molding, and a glass molding die having the coating.
2. Description of Related Art
In a molding die for a glass molded component such as a glass lens, improvement in mold releasability of glass has been investigated by covering a molding surface of a die base with a diamond-like carbon film (DLC film) or a noble metal series coating. For example, patent literature 1 describes a glass molding die having a transparent carbon film on a surface of a die base, the film having a carbon content of 95 at % or more, and Knoop hardness number in a range of 3000 to 7000. Patent literature 2 describes a glass molding die formed with a DLC film of which the density is changed continuously or stepwise. Patent literature 3 describes a fact that a molding surface of a base is covered with a protective film including any one of metals or metal alloys of Pt, Ir, W, Re, Ta, Rh, Ru, and Os, thereby durability and stability of a die are improved.
[Patent Literature 1]
JP-A No. 2003-89533.
[Patent Literature 2]
JP-A No. 2003-137565.
[Patent Literature 3]
JP-A No. 2003-26429.